We still continue to induce new chromosomal inversions in mice using TEM, to establish their linkage relationships, and to establish them when possible in "balanced-lethal" test systems for detecting recessive mutations. Particularly, we will continue to use the balanced-lethal system involving inversion In(1)1Rk to detect recessives induced in sperm and spermatids. The recessive lethal uncovered by this system will be studied for its genetic location, its time of lethality, and its possible effect in heterozygotes. We shall continue to study the mechanism by which reduction in recombination is achieved in these paracentric inversions without loss of fertility. Also we will study the effects of inversions on crossing-over in other chromosomes. Banding patterns of two of the inversions show the extent of the inverted segments. We will continue to use the new chromosomal staining techniques to study inversions and compare their physical lengths and locations with their genetic lengths and locations.